Packaging material and products comprising indicia-former which changes from a first visual condition to a second visual condition and indicates a characteristic of the package contents

ABSTRACT

Packaging materials, in particular, film and products that are marked with an energy sensitive indicia-former. The film has at least one heat sensitive indicia-former on at least part of the film. The film comprises a thin film substrate which is substantially transparent to radiant energy. Associated with at least part of the film substrate is an absorbent material which is sufficiently opaque to radiant energy to absorb said radiant energy and convert the radiant energy into heat energy. The indicia-former undergoes conversion from a first visual condition to a second visual condition upon exposure to heat energy from the absorbent material. The film is used preferably as a shrink wrap of the open top of drink containers and to identify the contents of the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/387,366, filed Jun. 10, 2002, and U.S. patentapplication Ser. No. 10/183,415, filed Jun. 28, 2002, both of which areincorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention pertains generally to packaging material andproducts which comprise (a) a substrate; and (b) an energy sensitiveindicia-former carried by the substrate. The invention also pertains, inparticular, to the use of such indicia-former on containers, having thecapability of indicating the contents of such containers.

BACKGROUND OF THE INVENTION

[0003] In numerous instances, products are made and packaged that do nothave markings that would be useful, for example, to identify theproduct, parts of the product or how to use the product. This is alsotrue for packaging. Product identifiers on packaging material such aslabels require time to complete and affix to the package, particularlyif used in fast food preparation.

[0004] In fast food outlets, convenience stores and the like, beveragedispensing machines are used which are capable of dispensing a number ofbeverages of different brands and flavors. These beverages are usuallypoured into disposable paper cups having advertising printed thereon,but bearing no markings to identify the cups' contents.

[0005] When a beverage order includes a number of different brandsand/or flavors, it is extremely difficult to determine the contents ofeach cup by visual inspection. Identification is further complicated bythe placement of thermoformed lids over the cups to prevent spillage.

[0006] As a consequence of this problem, mixups occur and customers getthe wrong beverage and do not discover the error until they taste it.

[0007] One way in which this confusion can be avoided is by using papercups of different colors or having different designs or markingsthereon. However, this requires a large inventory of cups, and theperson filling the order must be attentive to selecting the appropriatecup in order to avoid the error of filling the selected cup with theincorrect beverage.

[0008] Other ways of solving this problem include the use of labelsaffixed to the outer surface of the container or thermoformed lidshaving manually deformable buttons identifying drinks of various kinds.A further approach is marking the identity of the drink onto thecontainer or its lidding with a pen, i.e., by circling the drink type orchecking or box a dot next to a specific drink type. These solutionsrequire an inventory of container labels or lids and consistentlyattentive servers.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the invention to provide aproduct comprising a substrate and an energy sensitive indicia-formercarried by said substrate that undergoes conversion from a first visualcondition to a second visual condition.

[0010] It is another object of this invention to provide a packagingmaterial which comprises such energy sensitive indicia-former. It is afurther object of this invention to provide a packaging material whichshrinks in a controlled fashion upon exposure to heat of appropriateintensity, i.e. a shrink wrap material, thereby serving as a replacementfor plastic lids as closures for drink containers.

[0011] It is a further object of this invention to provide a closurewhich comprises as the heat sensitive indicia-former, thermochromic inkthat is converted from a first visual condition, preferably a visuallyindistinct, low contrast condition, to a second visual condition,preferably a visually distinctive, high contrast condition, whenundergoing a temperature change. The first visual condition ispreferably white. The second visual condition is preferably black oranother dark hue, so that the conversion from the first to the secondcondition is clearly visually perceptible, thereby enabling the use ofthe ink as a marker of the contents of the container to which theclosure is applied.

[0012] These and other objects are achieved by the packaging materialand products of the present invention which comprise (a) a substrate and(b) an energy sensitive indicia-former carried by the substrate, whichundergoes conversion from a first visual condition to a second visualcondition upon exposure to heat energy. A preferred embodiment of theinvention is a flexible packaging material which comprises (a) asubstrate that is substantially transparent to radiant energy, (b) anenergy absorbent material associated with at least a portion of thesubstrate, the absorbent material being sufficiently opaque to radiantenergy to absorb and convert radiant energy into heat energy, therebyraising the temperature of the absorbent material, and (c) an energysensitive indicia-former carried by said substrate which undergoesconversion from a first visual condition to a second visual conditionupon an increase in temperature resulting from exposure to heat energyfrom the absorbent material. In a preferred form, the packaging materialis a flexible film used to cover open-top containers. Other aspects ofthe invention include a method of manufacturing the above-describedpackaging and open-top containers covered by the above-describedclosures, and a method of filling an open-top container with a beverageand sealing the container with such closures.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 illustrates a configuration used for the indicia-former.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The invention has many applications. These include use of theindicia-former in packaging, product marking, decorative and labelingmaterial and as a barrier material to protect articles from damage from,for example, water, heat, cold and radiation. The products to be markedcan be any product to which the indicia-former can be affixed. Thepackaging may be any material continuously used for packaging, such aspaper, dimensionally stable materials such as cardboard and heatsensitive packaging such as polyurethane or transparent clam shells usedto hold take-out food. The packaging material may also be a film, andpreferably a flexible film.

[0015] The present invention will be described below with references tothin film closures which are preferably transparent. A particularlypreferred type of film is shrink film, commonly referred to as “shrinkwrap film.” It should be understood, however, that the packagingmaterial of the invention may also be embodied in a variety of otherforms, such as thermoformed lids, packaging for construction materials,paper goods and pharmaceutical containers.

[0016] End uses of these films include food packaging (for example,oxygen and moisture barrier bag for frozen poultry; prime meat cuts andprocessed meat and cheese products for preservation of freshness andhygienics) and non-food packaging (for example, “overwraps” forprotecting goods against damage, soiling, tampering and pilferage)during transporting, distribution, handling and display. A typical enduse is in retail sales where the films are wrapped air-tight aroundsingle or multiple items of compact disks, audio/video tapes, computersoftware boxes, magazines, confectionery, boxed products, single servebowls, etc. Another common end use is in wholesale marketing, wheremultiple containers of bottled and canned goods such as beverages,condiments and personal hygiene products are sold in bulk. Yet anotherexample is in courier shipping, where singular items of shrink-wrappedsporting goods and household appliances are safely transported withoutthe need for bulky protective cardboard cartons.

[0017] The term “shrink film” refers to a plastic wrapping film whichhas the capability of shrinking when it is heated to near the meltingpoint of the film. These films are commonly manufactured from plasticresins such as polyvinyl chloride (PVC); polypropylene (PP); linear-lowdensity polyethylene (LLDPE); low density polyethylene (LDPE); highdensity polyethylene (HDPE); copolymers of ethylene and vinyl acetate(EVA); copolymers of ethylene and vinyl alcohols (EVOH); ionomers (e.g.,SURLYN®, a registered trademark of E. I. duPont de Nemours and Co.,Wilmington, Del.); copolymers of vinylidene chloride (e.g., PVDC, SARAN,a trademark of the Dow Chemical Company); copolymers of ethylene andacrylic acid (EAA); polyamides (PA); polyester, polystyrene, nylon andcopolymers of ethylene and octene.

[0018] Film Substrate

[0019] Films particularly suitable for this purpose are flexible andsubstantially transparent to radiant energy. It will be appreciated bythose skilled in the art that the thickness of the film can be variedwithout adversely affecting the operation of the present invention. Forcertain applications, when greater strength is required, substantialfilm thickness may be appropriate, such as 200-gauge (0.05 mm) and more.Considerations such as price, tear resistance, degree of shrink andclarity will affect the selection of an appropriate film and thicknessto suit the commercial objective to be met. When used in contact withfood or beverage products, the film should be approved by theappropriate regulatory authorities.

[0020] If the film is a shrink wrap film, the preferred shrink filmsubstrate will have shrink characteristics suitable for the givenpackaging objectives. Some of these characteristics include the degreeand orientation of the shrink and whether the shrink is to occur in bothor only in one direction. Most common commercially available shrink filmsubstrates are substantially transparent, meaning that light, infraredradiation and other forms of radiant energy pass through the substratewith very little, if any, absorption. In this case, substantiallytransparent means that at least 75% and preferably more than 90% ofradiant energy passes through said film. Such transparency has led tothe utilization of a heat absorbing medium, in physical contact with thefilm, to provide sufficient heat transfer to cause the desired shrink. Apreferred film is a bi-axially oriented thin shrink film, having apreferred thickness of between approximately 50 to 150-gauge (0.0127 mmto 0.0381 mm) with the most preferred range being from 60 to 75-gauge(0.0152 mm to 0.0191 mm). Films meeting these specifications are a75-gauge (0.0191 millimeter). CLYSAR® polyolefin shrink film sold byBernis Corporation of Minneapolis, Minn. and a 75-gauge 0.0191millimeter Exfilm™ polyolefin shrink film sold by Intertape Corp. ofBradenton, Fla.

[0021] An alternate film is a shrink film that is made of polyvinylchloride and sold under the trade name #2024 REYNOLON®, a trade name ofReynolds Metals Company of Richmond, Va. Such films are disclosed inU.S. Pat. No. 6,291,037 B1 to Bakker, the contents of which areincorporated by reference herein.

[0022] Energy Absorbent Material

[0023] The energy absorbent material used in practicing this inventionis a material which is adapted to be associated with at least a portionof the film substrate and is sufficiently opaque to absorb energy,preferably radiant energy. Radiant energy includes electromagneticenergy. See The Condensed Chemical Dictionary, 8^(th) Edition, Revisedby Hawley, Gessner G. (Van Nostrand Reinhold Company, New York, 1971) p.750, in which radiation is defined as “energy in the form ofelectromagnetic waves (also called radiant energy or light).” The energyabsorbent material functions to convert radiant (electromagnetic) energyinto heat energy, thereby causing an increase in temperature of thefilm.

[0024] The absorbent material may be formed on the film by a variety ofwell-known methods such as printing means (flexographic, rotogravure,screen, transfer, etc.), brushing, spray coating, electrostatic coating,electrodeposition coating, flow coating, roller coating, dip coating,and the like. Printing is the preferred method (e.g., using flexographicor rotogravure techniques). The energy absorbent material includes atleast one radiant energy absorbing component such as carbon black,graphite, iron oxide or the like. It will be appreciated by thoseskilled in the art that while certain specific energy absorbingmaterials have been identified, other material will also be suitable.What is desired is that the energy absorption rate of the material besufficient so that upon exposure of the material to radiant energy, theheat generated will cause the desired degree of shrinkage of the filmsubstrate in a predetermined amount of time.

[0025] In some cases, such films may require special treatment to bemade more adaptable to printing of the energy absorbent materialthereon, such as the application of a charged electric field, known ascorona treating, which is done before printing to ensure adhesion of theabsorbent material, and its carrier vehicle, if any. Other methods ofpromoting adhesion of the absorbent material include flame treatment orchemical primer application. For other films, such as polyvinyl chlorideshrink films, corona treating is not necessary for good printingresults.

[0026] In an alternate embodiment, the absorbent material may bephysically incorporated into the film substrate and absorbs the radiantenergy from within the film. This latter approach is less preferred toprinting the absorbent material onto the film, since incorporating theabsorbent material into the film may change the heat shrinkcharacteristics of the film, such as flexibility, degree of shrink andthe like.

[0027] According to the present invention, radiant energy means energywhich may be transmitted from a suitable source to the absorbent layer,where it is absorbed to produce heat. In a preferred embodiment, theradiant energy is infrared radiation, which is efficiently absorbed bythe absorbent layer, but not the film. In this way, heat energy isprovided directly to the heat shrinkable film, thus avoiding thenecessity of using any other heating medium, such as hot water or air,as in the past to carry the heat to the film. Thus, radiant energy inthis context means any form of radiant energy that is transmissiblethrough a medium such as air, without being substantially absorbedthereby. In a preferred embodiment, the radiant energy is supplied by ahalogen bulb.

[0028] Carbon black provides good results when incorporated as theenergy absorbent material on or in the film substrate. In particular,carbon black responds readily to the radiant energy output of a halogenbulb, which emits energy primarily in the visible and near infraredspectrum. Carbon black is a standard pigment in printing inks. Thiscombined ability to blend with existing printing inks, and to absorbradiant energy such as infrared radiation, makes it well suited for usein the present invention.

[0029] A preferred energy absorbing material is carbonpigment-containing black ink sold by Coates Ink, a division of SunChemical, under the trade name Brazilia TN15787. This ink is readilyadapted for printing onto the film substrate. The Brazilia inks areavailable in many colors and are broadly usable as absorbing materialsaccording to the invention if the ink meets the requirements specifiedhereinabove. In a preferred embodiment, a reflective coating, preferablycomposed of white ink, is overlaid on the energy absorbent material inan amount sufficient to provide appropriate contrast with the areas theindicia-former, after it is caused to change from the first visualcondition to the second visual condition, so that the latter is moreeasily observed. A preferred white ink is also sold by Coates Ink underthe trade names Lunar TN12316 and Alfalam. The use of a white inkoverlay depends on whether a black or white background is more effectivein facilitating visual observation of the change in the indicia-formerfrom a preferred low contrast, first visual condition to the highcontrast, second visual condition.

[0030] Energy Sensitive Indicia-Former

[0031] As described hereabove, the energy sensitive indicia-formerchanges from one visual condition to a second visual condition. Changein visual condition would include but not be limited to change inappearance, hue, shade, perceptibility, including an enhancement inperceptibility, brightness, lightness, reflectiveness, absorptivity andcolor, including, for example, light gray to dark gray and white toblack.

[0032] The preferred indicia-former is a thermochromic pigment or dye,which may be dispersed in a suitable carrier. These thermochromicmaterials are preferably used in the form of a thermochromic inkincorporating a thermochromic pigment or dye in a carrier vehicle. Thethermochromic ink may be applied to the film substrate by the methodsidentified above for applying the absorbent material to the substrate.The preferred method is printing the thermochromic ink onto thesubstrate. The energy sensitive indicia-former is preferably anirreversible thermochromic ink that undergoes a change from white toblack when adequately heated. A preferred thermochromic ink, (sold bySherwood Technologies Limited of Nottingham, UK under the trade nameSherwood Type 90) is white below about 90° C. and undergoes anirreversible color change to black above about 90° C. Those of ordinaryskill in the art will understand there are a variety of ink systemscomprising one or more inks that can function as the radiant energyabsorbent material and as the heat sensitive indicia-former.

[0033] Those of ordinary skill in the art will understand that a varietyof ink colors can be used to obtain satisfactory results with thepresent invention and that a variety of energy sensitive indicia-formersother than thermochromic ink can also be used. Other inks that can beused in the invention as indicia-former are photochromic ink andelectrochromic ink, such as those disclosed in U.S. Pat. No. 5,830,529to Ross, the entire disclosure of which is incorporated herein byreference. Of course, photochromic and electrochromic inks, whenemployed as the indicia-former, would not require an absorbent layer.Instead, the indicia-former would be exposed directly to energy capableof causing the desired visual transformation of the indicia-former. Inaddition, those of ordinary skill in the art will understand that it isnot necessary to coat the entire film substrate with ink. Moreover,those of ordinary skill in the art will appreciate that ink patterns canbe used in applying the indicia-former to the substrate.

[0034] Preferred Applications of Absorbent and Indicia-Former Layers

[0035] As noted above, in a particularly preferred embodiment relatingto films used to cover drink containers, an absorbent materialcomprising an ink composition containing carbon black is printed ontothe film substrate. As this ink composition is black in appearance dueto its carbon black content, white ink, for example, is applied over theportions of the black ink on which the indicia-former is to be locatedto show the contents of the container, in order to provide appropriatecontrast for the indicia-former. Then the indicia-former is superimposedon the areas of white ink, preferably by printing.

[0036] There are, of course, numerous possible combinations of theabsorbent layer, optional contrast layer and energy sensitiveindicia-former that can be employed in carrying out the invention.

[0037] Those of ordinary skill in the art will understand that a varietyof ink concentrations can achieve satisfactory results in the presentinvention. The second ink which acts as an energy sensitiveindicia-former may be, as identified above, an ink that undergoesconversion from one color to another that contrasts with the color ofthe absorbent material upon a predetermined increase in temperature.Alternatively, it may be an ink that undergoes a different sort ofvisually observable conversion, such as a dye or luminescent pigmentthat is covered by a patch that disintegrates upon a specific increasein temperature. The requirements for the energy sensitive indicia-formerare that they undergo a conversion from a first visual state to a secondvisual state upon exposure to appropriate energy, and that such changesin visual state or condition are perceptible to the human eye.

[0038] Radiant Energy Source

[0039] According to one embodiment of the invention, the radiant energysource produces radiant energy by emitting light having wave lengths inthe visible and near infrared range. Those of ordinary skill in the artwill understand that the wave length of the energy emitted by theradiant energy source is not particularly critical, provided that theabsorbent material chosen is sufficiently absorbent within the range ofthe wave lengths emitted, so that conversion of the radiant energy intoheat energy and increased temperature of the film is reasonably rapid.

[0040] A preferred radiant energy source is a conventional halogen lampemitting light energy having wave lengths between about 600 nm to about1400 nm. It has been found that tungsten halogen lamps are a preferredradiant energy source. However, those of ordinary skill in the art willunderstand that a number of different radiant energy sources areavailable which produce sufficient visible and near infrared radiation,such as xenon arc lamps. The energy source is preferred to have a totalwattage of between 50 and 150 watts, and most preferably comprises one100-watt bulb. The wattage should be chosen to provide sufficient energyto shrink the film without burning through the film. One radiant energysource that has been successfully used is a Osram JC24V-100 WG6.35 fromOsram Sylvania, Inc., of Danvers, Mass.

[0041] In a preferred embodiment, the invention is used on packagingfilm which shrinks to form at least part of the package when exposed toheat. The packaging film includes a thin film substrate that contractsor shrinks when heated and which is substantially transparent to radiantenergy. The film also includes an absorbent material that issufficiently opaque to radiant energy to absorb and transfer to thesubstrate enough heat energy to cause the substrate to shrink when thefilm is exposed to a source of radiant energy. In a particularlypreferred embodiment, the packaging film performs the function of abeverage container lid.

[0042] In use, radiant energy is caused to impinge on the film coveringthe container. The film has several marking options, such as “soda,”“diet cola,” and “water,” imprinted on the film. Next to each option isan indicia area having absorbent and thermochromic ink layers.

[0043] In a particularly preferred form, the marking options printedonto the film have absorbent, reflective or contrast-enhancing andthermochromic layers. Accordingly, after the container is filled with aspecific beverage, radiant energy is directed to the film at thebeverage option selected. The radiant energy may be directed by indexinga variable mask situated, between the radiant energy source and theindicia-former. The radiant energy source may comprise one lamp or morethan one lamp. The radiant energy mask may have one orifice or severalorifices through which the radiant energy is directed to the film. Ifthe radiant energy is directed to the film at the beverage optionselected through one orifice, the radiant energy results in the heatingof the absorbent material precisely at the beverage option selected andthereby causes a localized increase in temperature of the indicia-formeridentifying that option. The increase in temperature causes theindicia-former identifying that option to change color (e.g., from whiteto black). The resultant black marking identifies the option selected,thus indicating the contents of the container. As radiant energy is notdirected at the indicia-formers identifying other drink options, thoseindicia-formers do not change color. Accordingly, the beverage optionselected is identified by the color change of the particularindicia-former identifying that option.

[0044] For example, if the container is filled with diet cola, theradiant energy is directed to, and causes the indicia-former identifying“diet cola” to change color, preferably from white to black. In thisembodiment, the indicia-former changes to a color that contrasts withthe background, so that the mark formed is easily identifiable. Theidentification marking can take numerous configurations. Preferredconfigurations are a circle enclosing the letter “x,” a check mark, oreven a word or words identifying the beverage. An illustration of one ofthese configurations, namely the circle enclosing the letter “x,” isshown in FIG. 1. Preferably, the source of the radiant energy ispositioned about 0.5 inch away from the film. In a most preferred form,the film is 0.932 inch from the center of the bulb filament and 0.464inch from the top of the bulb. If the radiant energy source is one100-watt halogen bulb, the film is exposed to the activated sourcetypically for one-quarter second, with the power applied at 30% ofcapacity.

[0045] Alternatively, radiant energy can be directed to the filmprecisely at the beverage options not selected so that the beverageoption selected would be the only option identified that did not undergoa change from one visual condition to a second visual condition. Thisprocess can be accomplished by directing the radiant energy throughseveral orifices in the variable mask. The orifices are aligned toensure that the radiant energy is directed to the film precisely at theindicia-former identifying the beverage options not selected.

[0046] In a preferred embodiment, this marking of the identification ofthe drink is carried out in the same sequence of operations during whichthe container is filled and the shrink wrap film cover is applied to theopen top of the container; however, the energy source used for themarking operation is distinct from the energy source used to shrink wrapthe cover over the open container.

[0047] The invention also includes a method of manufacturing the film ofthe invention. According to this method, an absorbent material isapplied onto at least a portion of a thin film substrate which issubstantially transparent to radiant energy. The absorbent material issufficiently opaque to radiant energy to absorb radiant energy andconvert it to heat energy. Then an energy sensitive indicia-former whichundergoes conversion from a first visual condition to a second visualcondition upon exposure to heat energy is applied onto the filmsubstrate. The preferred methods of application are by printing.

[0048] The invention also is directed to drink containers covered byheat shrinkable flexible films. According to this embodiment of theinvention, an open-top container is covered by a heat shrinkable,flexible packaging film having at least one heat sensitiveindicia-former on the surface thereof. The film material comprises athin film substrate which is flexible and contracts when heated, andwhich is substantially transparent to radiant energy, thereby remainingsubstantially unchanged by radiant energy. An absorbent materialoverlays at least a portion of the film substrate. The absorbentmaterial is sufficiently opaque to radiant energy to absorb and convertradiant energy into heat energy. This heat energy causes the heatsensitive indicia-former carried by the film to undergo conversion froma first visual condition to a second visual condition. This change invisual condition preferably occurs at a temperature below that at whichthe film is caused to shrink.

[0049] The invention is further directed to a method of preparing andsealing beverage containers. According to this embodiment of theinvention, an open-top container is filled with a beverage. The open-topcontainer is then covered with the film of the invention. The filmmaterial is then subjected to energy, which is converted to heat energy.The heat energy causes the film material to shrink to form a seal overthe open top, and the indicia-former is thereafter exposed to heatsufficient to transform it from the first visual condition to the secondvisual condition. Alternatively, the sealing step can be carried outsimultaneously with or after the step of transforming the indicia formerfrom a first visual condition to a second visual condition.

EXAMPLE 1

[0050] A test was performed to confirm the ability of the combination ofthe thermochromic and absorbing inks to form in the indicia-former afterit undergoes exposure to radiant energy in the form of a lightbulb. A75-gauge CLYSAR film manufactured by Bernis Corporation was printed withan absorbent material consisting of a black ink that contains carbonpigment sold under the name Brazilia TN15787 by Coates Ink, a divisionof Sun Chemical. Then a white ink sold by Coates Ink under the tradename Lunar TN12316 was printed over discrete portions of the black layerof absorbent material to provide indicia areas showing the various typesof drink options, resulting in each indicia area having a gray colorwhich serves to provide a contrasting background for the indicia formedupon conversion to the second visual condition. Next, an indicia-formercomposed of a white thermochromic ink manufactured by SherwoodTechnologies, LLD, Nottingham, UK, under the trade name Sherwood Type 90was printed over each gray-colored indicia area. The resulting indiciaareas were gray in color.

[0051] The film was exposed to a 350-watt halogen lightbulb, causing thethermochromic ink to turn from gray to black. The change in color of theindicia area was visible, but it was felt that the contrast could beimproved as described in EXAMPLE 2

EXAMPLE 2

[0052] The test procedure used in EXAMPLE 1 was repeated, except thatadditional white ink was provided for contrast on each indicia area,resulting in the indicia area having a white appearance relative to thegray appearance in EXAMPLE 1 above. Then the thermochromicindicia-former was added over the white layer and exposed to the same350-watt halogen lightbulb, causing the indicia-former to change fromwhite to black. Accordingly, the color change of the thermochromic inkin EXAMPLE 2 was more pronounced and easier to see.

EXAMPLE 3

[0053] The film substrate was treated with the absorbent ink for radiantenergy absorption, white ink to provide contrast and thermochromic inkas the indicia-former, as in EXAMPLE 1. The treated film was exposed tothe 350-watt halogen lightbulb for one-half second at a distance of 0.5inch. Following such exposure, the thermochromic layer changed fromwhite to black.

EXAMPLE 4

[0054] A packaging film was prepared as in EXAMPLE 3. The period ofexposure of the treated film to the 350-watt halogen lightbulb at adistance of 0.5 inch was changed from 0.5 second to 1.0 second. Theresulting heat melted the film, causing a hole to form in the film,indicating over-treatment.

EXAMPLE 5

[0055] The film of EXAMPLE 1 was exposed to radiant energy from a100-watt halogen bulb for one-quarter of a second. The halogen bulb wasoperating at 30% of full power (duty cycle energized 30% of the timeduring activation period). Radiant energy was applied to the film at adistance of 0.5 inch. These conditions resulted in the transformation ofthe thermochromic ink from white to black, without any noticeabledeleterious effect on the thermochromic ink layer.

EXAMPLE 6

[0056] The film of EXAMPLE 2 was exposed to radiant energy from a100-watt halogen bulb for one-quarter of a second. The halogen bulb wasoperating at 30% of full power (duty cycle energized 30% of the timeduring activation period). Radiant energy was applied to the film at adistance of 0.5 inch. These conditions resulted in the transformation ofthe thermochromic ink from white to black, without any noticeabledeleterious effect on the thermochromic ink layer.

EXAMPLE 7

[0057] The film of EXAMPLE 1 was treated with the black energy absorbentink, two layers of white ink for contrast and thermochromic ink. Thethermochromic ink was applied in the configuration of a circle enclosingthe letter “x.” The film was exposed to radiant energy from a 100-watthalogen bulb for one-quarter of a second. The halogen bulb was operatingat 30% of full power (duty cycle energized 30% of time during activationperiod). Radiant energy was applied to the film of a distance of 0.5inch. The condition resulted in the transformation of the thermochromicink from white to black, resulting in a very distinct circle enclosingthe letter “x.”

[0058] Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only with a true scope andspirit of the invention being indicated by the following claims.

We claim:
 1. A packaging material which comprises: a) a substrate; andb) at least one indicia-former carried by said substrate which undergoesconversion from a first visual condition to a second visual conditionupon exposure to heat energy.
 2. The packaging material according toclaim 1, wherein the material is flexible.
 3. The packaging materialaccording to claim 1, wherein the material is dimensionally stable. 4.The film according to claim 1, wherein the absorbent material comprisesat least one radiant energy absorbing component selected from the groupconsisting of carbon black, graphite and iron oxide.
 5. The flexiblematerial according to claim 1, wherein the indicia-former undergoes achange in perceptibility.
 6. The flexible material according to claim 1,wherein the indicia-former undergoes a change in appearance.
 7. Theflexible material according to claim 1, wherein the indicia-formerundergoes a change in hue.
 8. The flexible material according to claim1, wherein the indicia-former undergoes a change in shade.
 9. Theflexible material according to claim 1, wherein the indicia-formerundergoes a change in brightness.
 10. The flexible material according toclaim 1, wherein the indicia-former undergoes a change in lightness. 11.The flexible material according to claim 1, wherein the indicia-formerundergoes a change in saturation.
 12. The flexible material according toclaim 1, wherein the indicia-former undergoes a change in color.
 13. Theflexible material according to claim 1, wherein the indicia-formerundergoes a change in reflectiveness.
 14. The flexible materialaccording to claim 1, wherein the indicia-former undergoes a change inabsorbtivity.
 15. The flexible material according to claim 1, whereinthe indicia-former undergoes a change from white to black.
 16. Theflexible material according to claim 1, wherein the indicia-formerundergoes a change from light gray to dark gray.
 17. The film accordingto claim 1, wherein the indicia-former is configured to comprise acircle enclosing the letter “x.”
 18. The film according to claim 1,wherein the indicia-former is configured to comprise a check mark. 19.The film according to claim 1, wherein the indicia-former is configuredto comprise words identifying beverage options.
 20. The film accordingto claim 1, wherein the heat sensitive indicia-former comprisesthermochromic ink.
 21. The film according to claim 20, wherein thethermochromic ink undergoes conversion from white to black upon exposureto heat energy from the absorbent material.
 22. The film according toclaim 20, wherein the thermochromic ink is applied onto the filmsubstrate by printing.
 23. The film according to claim 22, wherein thethermochromic ink is applied onto the film substrate by flexographicprinting.
 24. A product which comprises: a) a substrate; and b) at leastone indicia-former carried by said substrate which undergoes conversionfrom a first visual condition to a second visual condition upon exposureto heat energy.
 25. A flexible material which comprises: a) a thin filmsubstrate which is substantially transparent to radiant energy; b) anabsorbent material associated with at least a portion of the substrate,said absorbent material being sufficiently opaque to radiant energy toabsorb said radiant energy and convert said energy into heat energy; andc) at least one indicia-former carried by said film substrate whichundergoes conversion from a first visual condition to a second visualcondition upon exposure to heat energy from said absorbent material. 26.A heat-shrinkable flexible packaging film, said film having at least oneenergy sensitive indicia-former on the surface thereof, said filmcomprising: a) a thin film substrate which is flexible and shrinks whenheated, and which is substantially transparent to radiant energy,thereby remaining substantially unchanged on exposure to radiant energy;b) an absorbent material associated with at least a portion of saidsubstrate, said absorbent material being sufficiently opaque to radiantenergy to absorb said energy and convert said radiant energy into heatenergy, with said heat energy being transferred to said indicia-former;and c) said energy sensitive indicia-former carried by said film beingcaused to undergo conversion from a first visual condition to a secondvisual condition upon exposure to said heat energy.
 27. The packagingfilm according to claim 26, wherein the temperature at which the energysensitive indicia-former undergoes conversion from one visual conditionto another is lower than the temperature at which said film is caused toshrink.
 28. The packaging film according to claim 26, wherein the filmsubstrate is selected from the group consisting of polyvinyl chloride,polyolefins such as polypropylene, linear-low density polyethylene, lowdensity polyethylene, high density polyethylene, copolymers of ethyleneand vinyl acetate, copolymers of ethylene and vinyl alcohols, isonomers;copolymers of vinylidone chloride, copolymers of ethylene and acrylicacid, polyamides, polyesters, polystyrene, nylon and copolymers ofethylene and octenes.
 29. The packaging film according to claim 28,wherein the film substrate is a polyvinyl chloride or a polyolefin. 30.The packaging film according to claim 29, wherein the film substrate isa bi-axially oriented shrink film having a thickness of between about0.0127 millimeters and about 0.0381 millimeters.
 31. The packaging filmaccording to claim 26, wherein the absorbent material comprises at leastone radiant energy absorbing component selected from the groupconsisting of carbon black, graphite and iron oxide.
 32. The flexiblematerial according to claim 26, wherein the indicia-former undergoes achange in perceptibility.
 33. The flexible material according to claim32, wherein the indicia-former undergoes an enhancement inperceptibility.
 34. The packaging film according to claim 26, whereinthe heat sensitive indicia-former comprises an ink elected from thegroup of thermochromic pigment, thermochromic dye and thermochromic ink.35. The packaging film according to claim 34, wherein the heat sensitiveindicia-former comprises thermochromic ink.
 36. The packaging filmaccording to claim 35, wherein the thermochromic ink undergoesconversion from white to black upon an increase in temperature due toheat energy from the absorbent material.
 37. The packaging filmaccording to claim 26, wherein the heat sensitive indicia-former isapplied to the film substrate by printing.
 38. The packaging filmaccording to claim 37, wherein the thermochromic ink is applied onto thefilm substrate by flexographic printing.
 39. The packaging film of claim26, wherein the thermochromic ink is applied to the film surface bybrushing.
 40. The film according to claim 26, wherein the indicia-formeris configured to comprise a circle enclosing the letter “x.”
 41. Thefilm according to claim 26, wherein the indicia-former is configured tocomprise a check mark.
 42. The film according to claim 26, wherein theindicia-former is configured to comprise words identifying beverageoptions.
 43. A method of sealing a beverage in an open-top container,said method comprising the steps of a) filling the container with thebeverage; b) applying over the open top of the container theheat-shrinkable flexible packaging film of claim 26; and c) exposing thefilm to at least one radiant energy source, resulting in the conversionof the radiant energy to heat energy that causes the film to shrink andseal the open top of the container and change the indicia-former from afirst visual condition to a second visual condition.
 44. The methodaccording to claim 43, wherein the radiant energy sources used to shrinkand seal the film and to change the indicia-former from the first visualcondition to the second visual condition are distinct.
 45. The methodaccording to claim 43, wherein the radiant energy source is a halogenlamp.
 46. The method according to claim 43, wherein the radiant energysource is a tungsten halogen lamp emitting light energy having wavelengths of between about 600 nm and about 1400 nm.
 47. In combination,an open-top container, the open top of which is covered by aheat-shrinkable flexible packaging film, said film comprising: a) a thinfilm substrate which is flexible and shrinks when heated, and which issubstantially transparent to radiant energy, thereby remainingsubstantially unchanged by radiant energy; b) an absorbent materialassociated with at least a portion of said substrate, said absorbentmaterial being sufficiently opaque to radiant energy to absorb saidradiant energy and convert said radiant energy into heat energy; and c)an energy sensitive indicia-former carried by said film and comprisingan ink formulation which undergoes conversion from a first visualcondition to a second visual condition upon exposure to heat energyconverted from the absorbent material.
 48. The combination of claim 47,wherein the indicia-former undergoes conversion at a temperature belowthat at which said film is caused to shrink.
 49. The combination ofclaim 47, wherein the absorbent material comprises at least one radiantenergy absorbing component selected from the group consisting of carbonblack, graphite and iron oxide.
 50. The combination of claim 47, whereinthe heat sensitive indicia-former is selected from the group consistingof thermochromic pigment, thermochromic dye and thermochromic ink. 51.The combination of claim 47, wherein the heat sensitive indicia-formeris thermochromic ink.
 52. The combination of claim 47, wherein theopen-top container is a beverage container.
 53. The combinationaccording to claim 47, wherein the indicia-former is configured tocomprise a circle enclosing the letter “x.”
 54. The combinationaccording to claim 47, wherein the indicia-former is configured tocomprise a check mark.
 55. The combination according to claim 47,wherein the indicia-former is configured to comprise words identifyingbeverage options.
 56. A method of manufacturing a flexible filmpackaging material, said method comprising the steps of: a) applying toa thin film substrate an absorbent material being sufficiently opaque toradiant energy to absorb said radiant energy and convert said radiantenergy into heat energy; and b) applying to the substrate of the film aheat sensitive indicia-former which undergoes conversion from a firstvisual condition to a second visual condition upon exposure to heatenergy.
 57. The method according to claim 56, wherein application steps(a) and (b) are carried out by printing the absorbent material and heatsensitive indicia-former onto the film.
 58. A heat shrinkable flexiblepackaging film, said film having at least one energy sensitiveindicia-former on the surface thereof, said film comprising: a) a thinfilm substrate which is flexible and shrinks when heated, and which issubstantially transparent to energy, thereby remaining substantiallyunchanged on exposure to energy; and b) said energy sensitiveindicia-former carried by said film comprising an ink formulation whichundergoes conversion from a first visual condition to a second visualcondition upon exposure to energy.
 59. The heat shrinkable flexiblepackaging film according to claim 58, wherein the indicia-former isselected from the group consisting of photochromic ink andelectrochromic ink.